README.md

changemachine

ChangeMachine is a critical component in the
Steelmesh stack. It is responsible for
monitoring and responding to changes in a number of couchdb instances and
taking appropriate actions in response to those changes.

The implementation of ChangeMachine is reasonably simple thanks to the
flatiron neuron queueing library and
through leveraging changemate
notifiers.

Online Documentation

System Internals

Attempts to act intelligently when a machine does not have a process
event handler. In this case, items are queued in the ready state and
we make use of the
newListener
node event to wait for a process event to be connected. At this stage, similar
action is not taken if the process listener is removed.

Makes use of changemate notifier pause and resume methods to ensure
efficient operation even in the case of a massive _changes feed from
couch, etc. In the case that a notifier does not support these operations,
items will be queued.

On ChangeMate vs Follow

While at the present stage an implementation of ChangeMachine would have been
possible with the excellent follow library
the long term plan is to support monitoring changes from the filesystem and other
sources so work changemate has been integrated instead.

Alternative Systems

Some alternative systems that do similar things are:

banzai - Banzai looks like an excellent
system for processing documents through a number of various states.
Banzai's implementation has definitely influenced parts of ChangeMachine.

hook.io - If you are building, loosely-coupled, distributed
systems then hook.io is one of the best choices in the #nodejs space. There
are instances where ChangeMachine could perform a similar function to hook,
but in most cases ChangeMachine is designed for simpler scenarios.

kue - Job processor built around redis,
has a pretty admin panel to boot.

Additionally, as previously stated, ChangeMachine does not attempt to compete
with full-blown messaging and queuing systems and if you require a more
distributed system then be sure to check out the likes of RabbitMQ and 0MQ.

License(s)

MIT

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
'Software'), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.